Wire line tensioning device



Nov. 6, 1 951 R. R. cRooKsToN WIRE LINE TENSIONING DEVICE Filed March 1,1950 2 SHEETS-SHEET 1 COOLING PINS SHOCK ABSORBER TO BRAKE GYLS.

"ASTER GYL.

FIG. I. H

Van: ASSEMBLY A COOLING FINS BRAKE ASSEMBLY SPRING ASSEMBLY B 55 BRAKEonuu I snocx ABSORBER Robert R. Crooksfon,

ATTORNEY.

Nov. 6, 1951 R. R. CROOKSTON WIRE LINE TENSIONING msvxcs Filed March 1,1950.

BRAKE ASSEMBLY FIG. 3.

SPRING 38 Asssrau INVENTOR. Robert R. Crooksfon FIG. 4.

ATTORNEY.

Patented Nov. 6, 1951 WIRE LINE TENSIONING DEVICE Robert R. Crookston,Houston, Tex., asslgnor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N.J., a corporation of Delaware Application March 1, 1950, Serial No.146,977

Claims. I

The present invention relates 'to a device for maintaining apredetermined minimum tension on a wire line held in stretched relation.More particularly, the present invention relates to a device formaintaining a minimum tension on a wire line as the wire line is reeledonto a spool.

In the level winding" of wire line onto spools, a number of essentialrequisites are recognized, among the most important of which are firstand second layer preparation, maintenance of proper fleet angle, andmaintenance of minimum tension. For example, the Roebling Handbook,published by John A. Roeblings Sons Co., a wire line manufacturer,stipulates direction of first layer helix in accordance with directionof line winding and laying of the rope. Roebling, as well as other wireline manufacturers, recognizes that fleet angles should be maintainedequally at between as a minimum per side and 1 as a maximum per side.This simply means that the arcs subtended by the wire line as it travelsacross the spool should exceed 1 and be less than 3 and that the lineitself be the arcs perpendicular bisector when the line is in themid-spool position.

Although wire line manufacturers, as well as field users, recognize theindispensability of minimum tension for successful level winding,"no'adequate steps have been taken by field users for satisfying thisrequirement. The contingency necessitating the maintenance of a minimumtension is that a heavy load on the line in an outer layer of the reeltends to cause the line under tension to "cut into" any layers belowthat which are loosely spooled or wrapped. For example, if the first orsecond layer is loosely wrapped, successive layers may not cut intothese layers until eight or ten or more layers are wrapped onto thespool. This condition can be corrected only by unreeling all the layersalready on the spool and properly re-winding the wire line onto thespool.

Operators of rigs for drilling boreholes into subsurface formations areimportant users of wire lines. Such lines are used for various purposessuch, for example, as swabbing, pulling cores, taking pictures, logging,etc. These lines must be wound and unwound from time to time ontospools, drums, or reels. It will be appreciated that the tension on theline as it is rewound will actually be less than, or at least differentfrom, that tension required to comply with the conditions of "levelwinding unless a tensioning means is intentionally provided.

The object of the present invention is to provide a tensioning devicewhich will maintain a minimum tension on a wire line which is beingwound onto a drum reel or spool when the wire line is being normallyused for such operations as swabbing, pulling cores, taking pictures.etc. A further object is to provide a tensioning device which willmaintain a minimum of wire line tension forthe operation of stringingnew lines. A further object is to provide a tensioning device which willpermit a wire line to be unwound from a spool without maintaining anytension thereon but which will permit a minimum tension to be maintainedon the wire line as it is being wound onto the spool or drum. A furtherobject is to provide a tensioning device which will maintain a minimumtension on a wire line so that this requisite of "level winding" can beaccomplished in the field.

The tensioning device of the present invention consists essentially of arotatable shaft flexibly supported at its opposite ends by biasingmeans, such as springs, above a frame member. A sheave is mounted on theshaft for free rotation on the shaft in one direction and is adapted forengaging with the shaft and for rotating the shaft when the sheave isrotated in the opposite direction. A braking assembly is mounted on theshaft on each side of the sheave. This braking assembly may beconventional in nature and may consist of a brake drum attached to theshaft and brake shoes adapted to engage with and disengage from thebrake drum. The braking assemblies are adapted to be energizedautomatically unless the tension in the wire line is suilicient to holddown the shaft and sheave against the compression of the biasing means.So long as the tension in the wire line is not sufficient to hold thesheave and shaft down against the compression of the biasing means, thebraking assemblies provide suflicient braking force to result in thedesired tension. The sheave is adapted to receive on its outer peripherya sumcient number of turns of the wire line to assure the desiredminimum tension on the tight line of the wire line even though thetension on the loose line is small. The tension on the tight line isdetermined by the well known wire line and belt equation which is asfollows:

T1=tight line tension (pull on spool, drum, or

reel) Tz=1oose line tension (weight on free end of wire line) =Napierianlogarithm base u=friction coefllcient (about 0.15 for wire line on steelor brass sheaves partially lubricated) 0=angular contact on sheave inradians.

If it is assumed that 3 /2 turns of the wire line are taken on thesheave and if the value of friction coefficient u is taken to be 0.15,the value of Ti in the foregoing equation is found to be:

This example demonstrates that a minimum of 2,000 pounds T1 tension isassured even for a dead weight of less than 100 pounds.

A tensioning device embodying the principles of the present invention isillustrated in the accompanying drawing in which:

Fig. 1 is a side view of one embodiment of the device of my invention;

Fig. 2 is a view of the embodiment shown in Fig. 1 taken along the line11-11;

Fig. 3 is a fragmentary view, partly in cross section, of theembodiments shown in Fig. 1 taken along the line III-III of Fig. 1;

Fig. 4 is a cross sectional view of a portion of the embodiment shown inFig. 3 taken along the line IV-IV of Fig. 3, the parts therein beingshown in their respective relations when the sheave is rotated in aclockwise direction;

Fig. 5 is also taken along the line IV-IV of Fig. 3 but shows the partstherein in their respective relations when the sheave is moved in acounter-clockwise direction;

Fig. 6 is a view, partly in cross section and showing in detail thebrake assembly A;

Fig. 7 is a detailed view of the brake cylinder illustrated in Fig. 6;and

Fig. 8 is a detailed view, partly in cross section, of the mastercylinder shown in Fig. 1.

Referring to the drawing in which like numerals designate like parts andlike letters designate like assemblies of parts throughout, IIdesignates a shaft which is supported at each of its ends above ahorizontal base by means of a compression spring assembly A and acompression spring assembly B. Mounted in the approximate center of theshaft is sheave I0. Mounted on shaft I I between sheave I and springassembly A is brake assembly A, and mounted on shaft II between sheaveI0 and spring assembly B is brake assembly B. Afiixed to shaft II oneach side of sheave I0 are spacing collars I00 and I00. These spacingcollars prevent the movement of sheave I0 longitudinally along shaft II.

Sheave I0 consists of a circular rim portion IOI defining a U-shapedvalley portion I02 on its outer periphery and a hub portion I03 joinedto the rim portion by means of spokes I04. A pair of bearings I and I05are disposed between the shaft I I and hub portion I03 of sheave I0, thesaid bearings being held in place by means of spacing rings I05 and I01,and closure plates I08 and I08. Closure plates I08 and I09 are securedto hub I03 and spacing rings I08 and I01 by means of a plurality ofbolts I I0.

Sheave I0 is mounted on shaft I I so that sheave I0 can be freelyrotated in one direction without also rotating shaft II, but which whenrotated in the other direction will also rotate shaft II. In order toaccomplish this purpose a, conventional free wheeling clutch mechanismI2 is mounted on shaft II within hub I03 of sheave I0.

Free wheeling clutch mechanism I2 consists of a member I3 mounted onshaft II for rotation therewith and is affixed to shaft II by suitablemeans such as by means of key I5. The outer surface I8 of member I3carries a plurality of radially spaced indentations I1 disposed alongits outer surface. In the drawing, four such indentations are shownalthough it will be understood that a lesser or greater number may bepresent. Each indentation I1 carries a roller bearing I8 which isnormally free to move within indentation I1 between member I3 and theinner surface IQ of the hub I03 of sheave I0. It will be understood, ofcourse, that a ball may be used instead of roller I8.

Free wheeling clutch mechanism I2 is so arranged with respect to'sheavel0 and shaft II that sheave I0 may freely rotate on shaft II in onedirection as, for example, in a clockwise direction as indicated by thearrow in Fig. 4 without turning member I3 and shaft II. This result isaccomplished by reason of the shape of indentation I1 in the outersurface I8 of member I3. This shape is most clearly shown in Figs, 4 v

and 5 which show grooves I1 having surfaces 20 and 2I of differentslopes with respect to a tangent drawn to the outer surface of member I3at the point where surfaces 20 and 2| join outer surface I6. In thisinstance. surface 20 is shown as forming an angle of nearly with thetangent while surface 2I forms a relatively acute angle. In any event,the slope of surface 20 is of such magnitude that roller I8 will notwedge between the outer surface I5 of member I3 and the inner surface I3of hub I83 of sheave I0 when sheave I0 is rotated in a clockwisedirection. On the other hand, surface 2I is of such an angle that rollerI8 will be caused to be wedged between surface 2I and the inner surfaceI9 of hub I03 when sheave I0 is rotated in a counter-clockwise directionas is shown in Fig. 5. Accordingly, when sheave I0 is rotated in aclockwise direction, member I3 and shaft II do not rotate; on the otherhand, when sheave I8 is rotated in a counter-clockwise direction, memberI3 and shaft II also rotate in a counter-clockwise direction incooperation with said sheave.

Each of extremities 21 and 21' of shaft II is supported above a framemember 32 by spring assembly A and spring assembly B, respectively. Thedetails of spring assembly A and spring assembly B are identical and,accordingly, only spring assembly A will be described in detail. Thedetails of spring assembly A are shown most clearly in Fig. 3.

Referring to Fig. 3, extremity 21 of shaft II is shown as beingcircumscribed by bearing housing 28, ball bearing 23 and ball bearing 30being positioned within said housing between shaft II and the housing.Bearing 28 and bearing 30 are spaced apart by spacer sleeve 3I. Nut 22abuts against bearing 23 and prevents lateral movement of shaft II withrespect to housing 28. It will be obvious that shaft II is freelyrotatable within housing 28, Bearing housing 28 is supported abovehorizontal frame member 32 by means of spring 33, the upper end 34 ofspring 33 abutting against a lower surface 35 of bearing housing 28;lateral movement of the upper end 34 of spring 33 is prevented bydownwardly projecting spring positioning member 35. The lower end 31 ofspring 33 abuts against horizontal frame member 32 and lateral movementof this end is prevented by upwardly projecting spring positioningmember 38, member 38 forming a part of frame member 32. Frame member 32is affixed to base member I22. Disposed on each side of spring 33 areshock absorbers 39 and 40 which are aillxed at their lower ends by meansof nuts 39' and 40', respectively, to frame member 32 and at their upperends to bearing housing 28 by means of connecting bolts 4| and 42,respectively, and nuts 43 and 44, respectively. Shock absorbers 39 and40 are not essential ele ments of the present invention but have beenfound desirable in that they make for smoother operation.

In like manner, extremity 21' of shaft II is supported above horizontalframe member 32 by means of spring assembly B, shaft II being heldagainst lateral movement within housing 28 of spring assembly B by meansof nut 22.

The foregoing description makes it apparent that shaft II and theelements mounted thereon can be moved toward horizontal frame member 32when suflicient pressure is exerted on the shaft to compress springs 33.However, the amount by which springs 33 can be compressed is limited bythe abutment of the lower surface 49 of member 49 on the upper surface32"01' frame member 32. Member 49 is a transversely extending memberinterconnecting vertically disposed yoke members 45 and 45'.

Yoke members 45 and 45' are identical in construction and, accordingly,only the details of member 45 will be given. Yoke member 45 defines apassage 46 and is mounted adjacent sheave I with shaft |I centrallydisposed in passage 46. Ball bearing 24 fits within opening 46' ofmember 45 and spaces member 45 away from shaft II, permitting shaft IIto rotate without also tending to rotate member 45. This is accomplishedby mounting the inner race 23 of ball bearing 24 on the spacing collarI00, the outer race 26 supporting member 45. Circulating balls 25 aredisposed between inner race 23 and outer race 26. Yoke members 45 and45' are joined at their lower ends 50 and 50', respectively, by means oftransversely extending member 49. The upper ends of yoke members 45 and45 may be held in spaced relation by means of laterally extending boltsI20 and I2 I.

Yoke member 45 defines horizontally extending arm 80 and a verticallyextending arm 8| which joins the end 82 of horizontally extending arm80. Yoke member 45' defines horizontally extending arm 80 and verticallyextending arm 8| vertically extending arm 8| joining horizontallyextending arm 80 and 82. A port 83 passes transversely through yokemember 45 at the juncture of horizontally extending arm 80 andvertically extending arm 8|. A similarly located port 83' traversesmember 45'. A vertically extending frame member 84 defines a pair ofspaced hinge members 85 and 86, each defining a port 81 and 88,respectively, in register with ports 83 and 83. A pin 89 passes throughports 83, 83, 81, and 86. Vertically extending frame member 84 forms apart of base member I22 and, accordingly, spaced hinge members 85 and 86are in fixed relation to frame member 32. Accordingly, pin 89 acts as apivot about which members 80 and 80 and 8| and 8| may move arcuately.The lower ends 90 and 90' of vertically extending members 8| and 8|,respectively, are pivotly connected with piston rod 9| by means of pivotmember 92.

Master cylinder I30 comprises cylinder housing I 3| which is afiixed toframe member 32 as by means of bolts I 32. Master cylinder housing |3|defines a reservoir I 33 and a cylindrical piston chamber I34,cylindrical piston chamber I34 cylindrical piston chamber I34communicating with-reservoir I33 by means of ports I35 and I36.

A refill port I31 communicates with reservoir I33 for recharging saidreservoir with hydraulic fluid. Piston rod 9| is joined at one end tomembers 8| and 8| by means of pivot pin 92 and its other bailed end I38fits slidably into socket I39 formed by piston I40. Piston I40 isslidably mounted within cylindrical piston chamber I34 in fluid-tightrelation with the inner walls thereof. Piston I40 is biased toward thepiston rod end of piston chamber I34 by means of spring MI. The head endof cylindrical piston chamber I34 defines an outlet port I43 whichfluidly communicates with conduits 11 and 11'.

When the head end I46 of piston I40 is to the right of port I36,hydraulic fluid in conduits I 43, 11, and 11 and in the head end ofpiston cylinder I34 is free to fiow into reservoir I33 through port I36.When, on the other hand, piston I40 is moved toward the head end ofpiston chamber I34 a suflicient distance to blank 01f port I36, then thefluid trapped in the head end of cylinder I34 is forced out through portI43, through conduits 11 and 11. The function of port I35 is to permitthe equalization of pressure in reservoir I33 and the piston rod end ofpiston cylinder I34. Spring I4I tends to bias piston I40 toward thepiston rod end of piston chamber I34.

A brake assembly A is mounted on shaft ll between yoke member 45 andbearing housing 28 of spring assembly A. A brake assembly B is mountedon shaft I between yoke member 45' and bearing housing 28' of springassembly B. Brake assembly B is identical in construction to brakeassembly A and, accordingly, the details of brake assembly A only willbe described. Brake assembly A includes a brake drum 52, the outersurface 'of which may carry a plurality of radially extending, angularlyspaced fins 53. Brake drum 52 is secured to annular disc 54 by means ofa plurality of bolts 55, annular disc 54 being mounted on shaft I I andaffixed thereto as by means of key 56. One edge 51 of annular disc 54abuts against spacer ring 58 which circumscribes shaft II which, inturn, abuts against inner race 23 of ball bearing 24, the other edge 59of annular disc 54 abutting against ball bearing 30 of spring assemblyA. A pair of arcuate brake shoes 60 and 6| carrying friction brakelining 62 and 62', respectively, on their outer arcuate surfaces isdisposed within brake drum 52, brake shoes 60 and 6| being so positionedthat brake linings 62 and 62' are in proximity to the inner cylindricalsurface 63 of brake drum 52. Ends 64 and 65 of brake shoes 60 and 6|,respectively, are secured to securing ring 41 by means of pivot pins 66and 66', respectively, a spacer 9 being interposed between said ends andsecuring ring 41. The other ends 61 and 68 of brake shoes 60 and 6|,respectively, are adapted to be moved to and from each other by asuitable means, such as by a conventional double acting hydraulicelement 69, to engage and disengage friction linings 62 and 62' withinner surface 63 of brake drum 52. A spring 5 interconnecting brakeshoes 60 and 6| is adapted to bias ends 61 and 68 of said shoes towardeach other.

Double-acting hydraulic brake cylinder 69, which is shown most clearlyin Fig. '1, consists of a cylinder 1| containing piston 13 connected bypiston rod 14 to brake shoe 60 and of piston 15 connected by piston rod16 to brake shoe 6|. Conduit 11 fluidly connects with the interior ofcylinder 1| into the space between pistons 13 and 15. Pistons 13 and 15are adapted to move slidably within cylinder 1| in fluid-tight relationit is to maintain upon the wire line.

with the inner walls thereof. Cylinder II is secured against movementwithin brake assembly A by attachment to securing ring 41 by means ofbracket 1 and bolts 8. The interior portion of brake assembly A isprotected against the entry of foreign matter, such as dust and grit, bymeans of brake rim which is appropriately secured to securing ring 41 asby means of bolts I and pins 66 and 66.

In Fig. 2 of the drawing, wire line I I0 is shown as wrapped around theouter U-shaped peripheral surface I02 of sheave I0. While three turns ofwire line 0 are shown on sheave I0, it will be appreciated that a lesseror greater number of turns may be wrapped upon sheave I0. The number ofturns which are wrapped upon sheave I 0 will depend upon the magnitudeof the tension In any event, U-shaped peripheral surface I02 of sheaveI0 must be sufficiently broad to accommodate at least one turn of wireline ||0.

Having fully described the various parts of the device of my inventionand their relation to each other, the operation of the device will nowbe described. When a wire line 0 is run over sheave I0 so as to rotatesheave I0 in a clockwise direction, sheave I0 free wheels, that is,rotates freely on shaft |I without rotating said shaft. Accordingly, thedevice of the present invention maintains no drag whatsoever upon wireline I I0 when it is passed over sheave I0 in such a manner as to rotatesheave I0 in a clockwise direction. On the other hand, when wire line H0is passed over sheave I0 in such a manner as to rotate sheave |0 in acounter-clockwise direction, rollers I8 of clutch mechanism I2 arewedged in between the inner surface I9 of sheave I0 and surface 2| ofmember I3 so that member I3 rotates in cooperation with sheave I0.Inasmuch as member I3 is affixed to shaft II by means of key I5, shaftII also rotates. Not only does the motion produced by drawing wire lineI I0 over sheave I0 rotate shaft I I, but the tension on wire line 0tends to move shaft II and the parts mounted thereon, including brakeassemblies A and B, downwardly against the upward thrust exerted bysprings 33 of spring assemblies A and B provided the weight suspended bythe loose line 0-1) of wire line 0 is sufficiently great. Rapid flex ofsprings 33 is prevented by shock absorbers 39 and 40. 'If the weightsuspended from the loose line IIO-b of wire line 0 is suflicientlygreat, springs 33 of spring assemblies A and B will be compressed untilthe lower surface 49 of member 50 abuts against the upper surface 32'-of frame member 32. The abutment of member 50 against frame member 32prevents, of course, further compression of springs 33. The letter aindicates the distance which member 50 moves while springs 33 move fromtheir non-compressed state when the loose line 0-1) of wire line 0 isnot under tension to the fully compressed state of springs 33, and themagnitude of a will depend, for a set of springs of given compressivestrength, upon the minimum tension it is desired to maintain on thetight line I I0-a of wire line I I0.

When member 49 abuts against frame member 32. brake linings 62 and 62'are disengaged from the inner surface 63 of brake drum 52 in a mannerwhich will be hereinafter described. However, while sheave I0 is beingrotated in a clockwise direction by movement of wire line I I0 thereoverand before member 50 abuts against frame member 32, brake linings 62 and62' of brake shoes 60 and BI, respectively, are in engaging contact withthe inner surface 63 of brake drum 52. The engagement of brake shoes 60and 6| with brake drum 52 provides a drag on the rotation of shaft II,and the magnitude of the braking force is so adjusted that the drag onshaft II results in the desired minimum tension in the tight line ||0-aof wire line 0, irrespective of the tension in the loose line IIO-b ofwire line ||0. Heat generated during periods of braking is dissipated bymeans of fins 53 disposed on the outer periphery of brake drum 52.

The magnitude of the braking force applied to inner surface 63 of brakedrum 52 by means of brake shoes 60 and 6| is automatically controlled byregulating the amount of fluid supplied to double-acting brake cylinders69 of braking assemblies A and B through conduits TI and 11',respectively. The amount of fluid supplied to double-acting cylinder 68is, in turn, controlled by master cylinder I30 which supplies hydraulicfluid to double-acting brake cylinders 69 in response to changes incompression of springs 33. When springs 33 are in their non-compressedstate, piston I40 of master cylinder I30 is at its forward limit oftravel toward the head end of piston cylinder I34 as indicated by thedotted lines in Fig. 8. When piston I40 is in this position, thehydraulic fluid in the head end of piston cylinder I34 has been forcedthrough conduits I43 and each of conduits "I1 and I1 into double-actingbrake cylinder 69 of brake assemblies A and B. At such time brake shoes63 and 6| of brake assemblies A and B are in their full engagingposition and provide maximum drag on the rotation of shaft II and thisdrag is of suflicient magnitude to produce the desired tension in thetight line IIO-a of wire line IIO. If the tension on the loose line|I0-b of wire line I I0 is only sufficient to partially compress springs33, then the braking force exerted by braking assemblies A and B is ofsuch magnitude as to supply the desired tension in the tight line I Il-aof wire line 0.

The magnitude of the braking force exerted by brake shoes 60 and 6| ofbrake assemblies A and B is correlated with the force exerted by springs33 of spring assemblies A and B by means of yoke members 45 and 45'.This follows from the fact that as springs 33 are compressed, yokemembers 45 and 45' move downwardly. Since horizontally extending arms 00and and vertically extending arms 8| and 0| of yoke members 45 and 45',respectively, are pivoted to upright frame member 04 by pin 03, thelower ends and 80 of vertically extending arms 0| and 8|, respectively.move arcuately in a direction away from master cylinder I30. Sincepiston rod SI of master cylinder I3! is pivotly attached to the lowerends 90 and 90 of vertically extending arms 3| and 0|, respectively, bymeans of pin 92, piston rod 9| also moves in the same direction.Follower spring I in master cylinder I30 forces piston I40 to move incooperation with piston rod 9|, thereby permitting hydraulic fluid toflow from doubleacting brake cylinders 69 of brake assemblies A and Bthrough conduits 'Il, I1, and I43 into the head end of piston cylinderI34 of master cylinder 30. The movement of lower ends 96 and 90' ofvertically extending members 8| and II, respectively, continues in theaforementioned direction until member 50 abuts against frame member 32,at which time piston I40 of master cylinder I30 reaches the full openposition indicated in Fig. 8, uncovering port I36. When port I38 isuncovered by piston I44,-hydraulic fluid in double-acting brakecylinders 69. conduits I1, 11', and I43 is no longer under pressure andis free to flow into reservoir I33 of master cylinder I30. Since nopressure is then being exerted against brake shoes 6| and GI bydouble-acting brake cylinders 69 of brake assemblies A and B, springretracts brake shoes 60 and BI into a fully disengaged position withrespect to brake drums 52. I

Master cylinder I30 may be refilled with hydraulic fluid from time totime through conduit I31 which fluidly communicates with reservoir I33.Port I35 permits the hydraulic fluid in reservoir I33 to have access tothe piston rod side of piston I40 so as to provide lubrication forpiston I40 in its travel within piston cylinder I34.

From the foregoing description it will be ob vious that by selectingsprings 33 of proper compressive strength and by correlating the brakingforces exerted by brake assemblies A and B with the compressive strengthof said sprin s, the device of my invention may be constructed so thatit will exert any desired minimum tight line tension on a wire line.

In the embodiment illustrated and described, hydraulic rather thanpneumatic brakes have been employed. It will be understood, of course,that pneumatic brakes will also function in the described combinationalthough hydraulic brakes are preferred because of the greater degree ofcompactness which can be secured through their use.

Having fully illustrated and described the present invention, what Iwish to claim as new and useful and desire to secure by Letters Patentis:

1. A device for maintaining a minimum tension on a wire line comprising,in combination, a rotatably mounted shaft supported by a plurality ofsprings in compression, a sheave mounted on said shaft for free rotationon said shaft in one direction and adapted for engaging with and forrotating said shaft when said sheave is rotated in the oppositedirection, said sheave being adapted to receive on its outer peripheryat least one turn of said wire line, a brake drum aifixed to said shaftfor rotation therewith, and a braking element adapted to be engaged withand disengaged from said brake drum in response to changes in the degreeof compre sion of said springs for resisting the rotary motion of saidsha t w en in enga ement with aid brake drum.

2. A device for maintaining a minimum tension on a wire line comprising,in combination, a rotatably mounted shaft supported by a plurality ofsprings in compression, a sheave mounted on said shaft for free rotationon said shaft inone direction and adapted for engaging with and forrotating said shaft when said sheave is rotated in the oppositedirection, said sheave being adapted to receive on its outer peripheryat lease one turn of said wire line, a brake drum affixed to said shaftfor rotation therewith, and a braking element adapted to be engaged withsaid brake drum for applying an alterable braking force whenever saidsprings exert a bias on said shaft less than that required to maintain aminimum tension on said wire line, said alterable braking force being ofsuflicient magnitude to maintain said minimum tenson, said brakingelement being adapted to be disengaged from said brake drum when saidsprings exert a bias on 10 said shaft suflicient to maintain a minimumtension on said wire line.

3. A device for maintaining a predetermined minimum tension on a wireline comprising, in combination, a frame member, a first spring mountedon said frame member with one end of said spring abutting against saidframe member, a second spring mounted on said frame member with one endof said spring abutting against said frame member, said second springbeing spaced from said first spring, a shaft rotatable about itslongitudinal axis mounted on said first and second springs, said springsbiasing said shaft away from said frame member, a sheave mounted on saidshaft for free rotation on said shaft in one direction and adapted forengaging with and for rotating said shaft when said sheave is rotated inthe opposite direction, said sheave being adapted to receive on itsouter periphery at least one turn of said wire line, a brake drummounted on said shaft for rotation therewith, a braking element adaptedto be engaged with said brake drum for applying an alterable brakingforce thereto when said springs exert a bias against said shaft lessthan that ,required to maintain said predetermined minimum tension onsaid wire line, said alterable braking force being of suflicientmagnitude to maintain said predetermined minimum tension, said brakingelement being adapted to be disengaged from said brake drum when saidsprings exert a bias suflicient to maintain said predetermined minimumtension on said wire line.

4. A device for maintaining a predetermined minimum tension on a wireline comprising, in combination, a frame member, a first helical springmounted on said frame member with one end of said spring abuttingagainst said frame member, a second helical spring mounted on said framemember with one end of said spring abutting against said frame member,said second helical spring being spaced from said first helical spring,a shaft rotatable about its longitudinal axis mounted on said first andsecond helical springs, said springs biasing said shaft away from saidframe member, a sheave mounted on said shaft for free rotation on saidshaft in one direction and adapted for rotating said shaft when saidsheave is rotated in the opposite direction, said sheave being adaptedto receive on its outer periphery a plurality of turns of said wireline, a brake drum mounted on said shaft for rotation therewith, saidbrake drum having a cylindrical surface coaxially arranged with andradially spaced from said shaft, a yoke member supported by said shaftand extending radially therefrom, said yoke member being pivotallyattached to said frame member and being arranged to limit the travel ofsaid shaft in its movement toward said frame member against the biasexerted by said springs, a first brake shoe having an arcuate frictionsurface engageable with the cylindrical surface of said brake drum, asecond brake shoe having an arcrate friction surface engageable with thecylindrical surface of said brake drum, one end of said first and secondbrake shoes being pivotally hinged to said yoke member, the other end ofsaid first brake shoe being attached to a first movable e ement arrangedwithin said double-acting hydraulic cylinder and the other end of saidsecond brake shoe being attached to a second movable element arrangedwithin said double-acting hydraulic cyl inder, a master cylindercontaining hydraulic fluid aflixed to said frame member, a piston 11slidably and aealably arranged in said master cylinder, said pistonbeing pivotaily'connected by means of a piston rod to said yoke memberand longitudinally movable within said master cylinder by said yokemember, a first conduit fluidly connectlnz said master cylinder withsaid first hydraulic cylinder, and a second conduit fluidly connectingsaid master cylinder with said second hydraulic cylinder.

5. A device for maintaining a minimum tension on a wire line comprising,in combination, a rotatably mounted shaft supported by flexible biasingmeans, a sheave mounted on said shaft for free rotation on said shaft inone direction and adapted for en aging with and for rotating said shaftwhen said sheave is rotated in the opposite direction, said sheave beingadapted to 12 receive on its outer periphery at least one turn of saidwire line, and braking means associated with said shaft and adapted tobe operatively connected with and disconnected from said shaft inresponse to changes in the degree of bias exerted by said biasing meansfor resisting the rotary motion of said shaft when operatively connectedwith said shaft.

ROBERT R. CROOKSTON.

REFERENCES CITED UNITED STATES PATENTS Name Date Chapman May 25, 1943Number

